硅灰对高强地聚物胶凝材料性能的影响

Influence of Silica Fume on Performance of High-Strength Geopolymer

以矿渣、粉煤灰和硅灰为原材料制备高强地聚物,利用单一质心设计法对原材料组成进行设计优化,研究了硅灰对凝结硬化过程以及对硬化浆体抗压强度的影响。结果表明:硅灰充分发挥了细颗粒作用,充填在矿渣和粉煤灰堆积空隙中,由此释放的激发剂提高了固体颗粒表面的液膜厚度,从而改善地聚物的流动性,降低浆体的触变性、屈服应力和塑性黏度;由于高活性,部分硅灰在强碱性溶液中快速溶解,使得激发剂中硅酸根离子浓度提高,碱度降低,从而使矿渣和粉煤灰的反应速率降低,减缓C—A—S—H凝胶形成,宏观上表现为凝结时间延长,加速期迟滞,反应热峰值和累计放热量降低,硬化体早期强度发展受到影响。当矿渣含量>50%、粉煤灰含量<30%且硅灰含量<30%时,地聚物砂浆强度超过100MPa,满足新拌性能要求,具有制备超高性能混凝土的可行性。

Slag, fly ash and silica fume were used as reactive aluminosilicate materials to prepare high-strength geopolymer. The influence of silica fume on the setting and hardening of geopolymer was particularly investigated based on the optimization of solid raw materials and activator compositions by a simplex centroid design method. The results show that silica fume can be used as a filler in the packing void between slag and fly ash particles, thus increasing the liquid film thickness due to the release of activator from the voids. This reduces the thixotropy of the paste as well as yield stress and plastic viscosity, thereby improving the flowability of geopolymer. A rapid dissolution of silica fume in a highly-alkaline activator increases the concentration of silicates and decreases alkalinity, leading to deceleration of the reactions of slag and fly ash and the formation of C-A-S-H gels with the prolongation of setting, the retardation of acceleration period, and the decrease of peak reaction heat rate and cumulative reaction heat. This affects the early reaction products and compressive strength development of geopolymer. The compressive strength of the resultant geopolymer reaches higher than 100 MPa with a good workability and reasonable setting time when slag content is more than 50%, fly ash is less than 30% and silica fume is less than 30%, indicating a possibility of producing geopolymer-based UHPC.